Simultaneous separation of inorganic anions and cations by using anion-exchange and cation-exchange columns connected in tandem in ion chromatography

Inorganic anions and cations in environmental waters were determined by ion chromatography. Stationary and mobile phases were examined for the simultaneous separation of both anions and cations. Cations detection by UV detection requires a mobile phase with a UV absorbing additive, which indirectly visualizes cations as negative peaks. Simultaneous separation of anions and cations were achieved when using an eluent that consists of inorganic acid with weak basic amino acid as additives. It was convenient to separate both anions and cations by coupling anion-exchange and cation-exchange columns in tandem. The order of the separation columns connected affected the elution profiles. When the eluent comprises of multiple anions and a single cation, the anion-exchange column should be connected in the upper stream, whereas when the eluent comprises multiple cations and a single anion, the cation-exchange column should be connected in the upper stream. Use of switching valves also allowed simultaneous separation of anions and cations in a single chromatographic run. In the present work, operating conditions were optimized for the simultaneous separation of anions and cations.     

Effect of Column Temperature on the Retention of Inorganic Anions and Organic Acids in Non-Suppressed Anion-Exchange IC

An investigation has been conducted into the effect of column temperature on the retention of inorganic anions and organic acids in non-suppressed ion chromatography on an anion-exchange column. Potassium biphthalate and p-hydroxybenzoic acid–tris–boric acid were used as mobile phases. The column temperature was from 25 to 50 °C. Endothermic and exothermic retention of inorganic anions were both observed when potassium biphthalate was used as mobile phase. When p-hydroxybenzoic acid–tris–boric acid was used as mobile phase, however, endothermic behavior only was observed. Moreover, for the two mobile phases, variation of the retention time of the system peaks with changing temperature was reversed. For retention of the organic acids, only endothermic behavior was observed with the two mobile phases. Variation of retention time was greater when p-hydroxybenzoic acid–tris–boric acid was used as mobile phase than when potassium biphthalate was used. These results indicated the exchange reaction in anion-exchange chromatography could be either endothermic or exothermic, depending on the solute and mobile phase ions involved. Different relative changes of retention time were observed for individual inorganic anions and organic acids with increasing column temperature. In general, variation of retention time with increasing temperature was greater for strongly retained inorganic anions and organic acids than for weakly retained species. Van’t Hoff plots for inorganic anions, organic acids, and system peaks were linear. Selectivity variation of the retention of inorganic anions and organic acids was achieved by changing the temperature. In achieving optimum separation of inorganic anions and organic acids, temperature was a valuable tool. To reduce the retention times of the ions and avoid interference from system peaks in non-suppressed anion-exchange ion chromatography with the two mobile phases, a low column temperature, for example, 35 °C, was best.     

Comparison of liquid chromatographic behaviors on N-methylimidazolium functionalized ZrO(2)/SiO(2)-4 and N-methylimidazolium functionalized SiO(2) stationary phases

A new stationary phase N-methylimidazolium functionalized ZrO(2)/SiO(2)-4 (Zr/SilprMim) has been prepared. The chromatographic property of this stationary phase is investigated by ion chromatography (IC) with inorganic and organic anions, and normal phase HPLC with basic compounds and hydroxybenzenes. The effects of pH and the strength of Lewis base of eluent on separation of anions are studied. This new stationary phase is also compared with a N-methylimidazolium functionalized SiO(2) stationary phase (SilprMim). The results show that this new stationary phase can be used in analysis of inorganic anions with great prospects. At the same time, successful separations of some organic anions can be obtained by using phosphate buffer solution as mobile phase. This new stationary phase also has a distinct advantage in the separation of basic compounds in normal phase. But due to the presence of Lewis acid sites on the surface of ZrO(2)/SiO(2)-4, Lewis bases such as hydroxybenzenes adsorb very strongly on this new stationary phase, and Lewis acid sites can be masked or modified by the eluent that contain Lewis base groups.     

Regeneration of tetrabutylammonium ion-pairing reagent distribution in a gradient elution of reversed phase ion-pair chromatography

The regeneration of ion-pairing reagent distribution on liquid chromatography columns after gradient elution has been well recognized as the cause for long column equilibration time, a major drawback associated with gradient elution reverse phase ion-pair chromatography. To date, the majority of studies have focused on optimizing the separation conditions to shorten the equilibration time. There is limited understanding of the ion-pairing reagent distribution process between the mobile phase and stationary phase in the course of gradient elution, and subsequent column re-equilibration. The focus of this work is to gain a better understanding of this process. An ion-pair chromatographic system, equipped with a YMC ODS C(18) column and a mobile phase containing tetrabutylammonium (TBA) hydroxide as the ion-pairing reagent, was used in the study. The TBA distribution profile was established by measuring its concentration in the eluent fractions collected during the gradient cycle using different column equilibration times with an ion chromatographic method. Furthermore, the analyte retention time was evaluated as the function of the column equilibration time and TBA concentration in the mobile phase. The column equilibration and its impact on the method robustness will also be discussed.     

Speciation of Cr(III) and Cr(VI) and separation of common anions by ion pair chromatography with trans-1,2-diaminecyclohexane-N,N,N',N'-tetraacetic acid

A reversed phase ion pair chromatographic method for the simultaneous determination of Cr species and common anions on a C(18)-bonded stationary phase was developed by using acetonitrile-water (2:98 v/v) containing 1.0 mM tetrabutylammonium hydroxide and 0.5 mM trans-1,2-diaminecyclohexane-N,N,N',N'-tetraacetic acid (DCTA) at pH 6.5 as mobile phase and UV-detection at 210 nm. Chromatographic parameters were optimized for separation of Cr(III)-DCTA complex, chromate and other anions. The detection limits were found as 8 ng/ml for Cr(III) and 35 ng/ml for Cr(VI). Under the optimum conditions, most other ions did not interfere. The method can be applied to separate a number of common anions simultaneously with the separation of Cr(III) and Cr(VI).     

CL-7402萃淋树脂分离富集铅的研究及其应用

通过静态和动态实验,研究了CL-7402萃淋树脂吸附铅的性能和减压微色谱柱分离富集铅的最佳条件。实验表明,此萃淋树脂吸附快,吸附容量大。在减压条件下,以1mol/LHBr为上柱介质,2mol/LHNO3为洗脱液,可使铅与铜、铁等金属离子快速分离。采用三溴偶氮胂光度法测定样品中的铅。     

Solving complex anion separation problems with a carbonate-hydrogencarbonate gradient

This paper describes the application of a new suppressor to solve complex anion separation problems with carbonate-hydrogencarbonate gradients. In addition to suppressing the mobile phase and enhancing the analyte signal like any other ion chromatography suppressor, the new DS-Plus suppressor removes carbonic acid from the suppressor effluent when carbonate-hydrogencarbonate mobile phases are used. This greatly reduces the background signal, enabling carbonate-hydrogencarbonate gradients. Since carbonate-hydrogencarbonate mobile phase has stronger eluting power than hydroxide or tetraborate, only dilute concentrations are needed to separate most anions. By adjusting the carbonate-hydrogencarbonate ratio in the mobile phase, various anion mixtures including those containing organic and inorganic anions with -1 to -3 charges can be separated on one or two columns, eliminating the needs for columns with special selectivity.     

Simultaneous ion-pair chromatography of inorganic anions and cations using on-column derivatization with chelating agents and UV detection

Six complexones have been investigated as on-column derivatizing agents for the simultaneous separation of inorganic anions and cations using ion pair chromatography. UV spectrophotometry at 210 nm has been applied for both the direct and the indirect detection of anions and anionic metal complexes. Under the experimental conditions used DCTA and DTPA have been practically applicable. Factors affecting the chromatographic behaviour of analyte ions have been studied. Chloride, nitrite, nitrate sulphate, chromate, molybdate, iron, chromium (III), copper (II), cobalt (II), nickel (II) and mercury (II) ions have been separated in 30 min with a mobile phase containing 1 mmol/1 TBA and 0.5 mmol/1 DCTA at pH 6.2 in acetonitrile-water (10:90 v/v). With DTPA as eluent and using pre-column derivatization of metal cations with DCTA eight anions and six metal cations can be separated. The detection limits are less than 0.1 mg/l for most of the investigated ions. Permanent address: Department of Analytical Chemistry, Vilnius University, Naugarduko 24, 2006 Vilnius, Lithuania     

Application of Iodine-Azide Reaction as Postcolumn Reaction in HPLC for Determination of 2-Thiobarbituric Acid

The reaction between iodine and azide ion induced by 2-thiobarbituric acid (TBA) has been utilized as a postcolumn reaction for chromatographic determination of this sulphur compound. The method is based on the separation of thiobarbituric acid on an Nova-Pak® CN HP column with an acetonitrile–aqueous solution of sodium azide mobile phase. The separation stage is followed by spectrophotometric measurement of the residual iodine (λ=350 nm) from the postcolumn iodine-azide reaction induced by thiobarbituric acid after mixing iodine solution containing iodide with the column effluent containing azide ions and the inductor. Chromatograms obtained for thiobarbituric acid showed negative peaks as a result of the decrease in absorbance of background. The detection limit (defined as S/N=3) was 0.16 pmol (22.9 pg) for thiobarbituric acid. Calibration graphs, plotted as peak heights or peak area vs. concentrations, were linear up to 1 nM.     

Anion separations for liquid chromatography using propylpyridinium silica as the stationary phase

This work describes the characterization and potential applications of a silica-based anion-exchange phase prepared by a two-step modification process that incorporates a propylpyridinium group. The effects of pH and eluent concentration on anion separation were examined using 150 mm × 3.9 mm HPLC columns packed with the new phase. The mobile phase pH values ranged from 3.8 to 6.6 using phthalic acid/Tris solutions. The best separation was achieved using 2.5 mmol L⁻¹ phthalate/2.4 mmol L⁻¹ Tris solution at pH 4.2 as mobile phase with non-suppressed conductivity detection. The new stationary phase was used for the separation of some inorganic and organic anions showing good resolution. The stability of the silica-based anion exchange phase was also evaluated.Analytical curves, for concentrations ranging from 0.25 to 10 mg L⁻¹ for the inorganic anions chloride, nitrite, bromide and nitrate, showed good linear correlations (r > 0.998). The method was tested with certified rainwater samples. The measured and certified values were in good agreement, indicating that the new phase holds significant promise for the analysis of these anions in environmental samples.     

纤维素衍生物手性固定相高效液相色谱法分离盐酸川丁特罗对映体

以纤维素三-(3,5-二甲基苯基氨基甲酸酯)为手性固定相(Lux Cellulose-1),建立了在正相色谱条件下直接分离盐酸川丁特罗对映体的高效液相色谱法。考察了乙醇、异丙醇等有机改性剂,三氟乙酸、二乙胺等流动相添加剂和柱温对对映体分离的影响。结果显示,酸性和碱性添加剂对对映体分离的影响最为显著: 添加二乙胺时两对映体无分离趋势;添加三氟乙酸时对映体保留强,且分离趋势明显;而同时添加三氟乙酸和二乙胺则两对映体分离显著改善,分离度可达4.0。优化后的色谱条件: 色谱柱为Lux Cellulose-1手性柱(250 mm×4.6 mm, 5 μm),流动相为正庚烷-乙醇-三氟乙酸-二乙胺(88:12:0.3:0.05, v/v/v/v),流速为1.0 mL/min,紫外检测波长为246 nm,柱温为25 ℃。该方法简便,快速,可用于左旋盐酸川丁特罗原料中右旋异构体杂质的检查。     

Novel imidazolium stationary phase for high-performance liquid chromatography

A new imidazolium anion-exchange phase immobilized on silica is synthesized. HPLC separations of common inorganic anions (IO3-, Cl-, NO2-, Br-, NO3-, I-, SCN-) have been performed using a HPLC column (200 mm x 4.6 mm I.D.) packed with this stationary phase, with a phosphate buffer solution as the mobile phase and UV detection at 200 nm. The effects of pH and concentration of eluent on the separation of anions have been studied. Chromatographic parameters are calculated and the results show that the new stationary phase is of significant potential for the analysis of these anions. Successful separations of some ordinary organic anions have also been achieved with the said stationary phase. Meaningfully, organic and inorganic anions can be determined simultaneously and satisfactorily with several neutral compounds using the column. The separation of some organic compounds including hydroxybenzenes, bases and amines by this stationary phase with only water as the eluent has been investigated.     

Evaluation on the adsorption capabilities of new chemically modified polymeric adsorbents with protoporphyrin IX

A novel stationary phase — phenylaminopropyl (PLA) bonded silica — is proposed for anion-exchange chromatography. Low basicity (pK_a about 2.5) attached to silica phenylaminopropyl groups allows a variation of surface density of protonated sites in the pH range from 2 to 5. This enables us to use the same column for the separation of anions having different affinity to anion-exchangers. The effect of mobile phase pH on conditional capacity of PhA-silica was studied. The hypothesis on dependence of ion-exchange selectivity on the column capacity is discussed. Suitability of PhA-silica for ion-chromatographic separation of organic and inorganic anions at different pH values of eluent was demonstrated.     

离子色谱法测定麻黄中的无机阴离子

建立了用单柱阴离子色谱测定麻黄中阴离子的方法。采用Shim Pack IC AI阴离子交换柱、2.5 mmol/L 邻苯二甲酸和2.4 mmol/L 三羟甲基氨基甲烷混合溶液为流动相、电导检测器在10 min内完成麻黄草中F-,Cl-, NO-2,Br-,NO-3, SO 2- 4的测定。该法具有良好的线性（相关系数为 0.999 2 ～ 0.999 7 ）和重复性（相对标准偏差小于1.92%）,回收率为96.6%～100.4%。方法简便实用,用于实际样品分析,所得结果令人满意。     

反相离子对色谱-电感耦合等离子体质谱联用技术测定水中痕量Cr(Ⅲ)与Cr(Ⅵ)

建立了反相离子对色谱(RPIPC)与电感耦合等离子体质谱(ICP-MS)联用技术快速分离测定水中痕量Cr(Ⅲ)和Cr(Ⅵ)的方法.通过考察流动相的pH值、离子对试剂及甲醇的浓度和EDTA的添加等对不同形态铬的保留时间及分离度的影响,确定当流动相组成为2.0 mmol/L TBA,5%(V/V)甲醇,pH=5.5时,Cr(Ⅲ)与Cr(Ⅵ)可达最佳分离.ICP-MS测定时选用碰撞池技术以消除40Ar12C+与35Cl16OH+对52Cr+的谱学干扰;进样100 μL时,Cr(Ⅲ)与Cr(Ⅵ)的检出限分别为0.15 μg/L和0.16 μg/L.加标回收率在93.6%～106.2%之间; RSD<4%(n=3).以本方法分析了某市自来水、雨水及某品牌纯净水中Cr(Ⅲ)与Cr(Ⅵ)的含量,结果令人满意.     

Chromatographic behavior of ion pair enantiomers of dansyl leucine cyclohexylammonium salt on a beta-cyclodextrin stationary phase and the effect of a competitive-binding mobile phase additive

The separation of dansyl leucine enantiomers on a beta-cyclodextrin stationary phase is significantly complicated by the association of the amino acid with its cyclohexylammonium counter ion, in a mobile phase of 80:20 (v/v) methanol-water. This produces very unusual chromatography, with two partially superimposed peaks observed for each enantiomer at lower column temperatures. The peak shape is attributed to the irreversible, oncolumn conversion of the ion pair (I) to the free, protonated (neutral) dansyl amino acid (II+H). Increasing the ionic strength of the mobile phase greatly improves the chromatography by transforming the solute species to enantiomers of II (the anionic, free amino acid). Van't Hoff plots are constructed for both species I and II (under different mobile phase conditions) to provide thermodynamic insight into the major enantioselective driving forces of separation. The chiral discrimination of the stationary phase is found to be primarily enthalpically driven for both solutes. Finally, 1-adamantanecarboxylic acid (ACA) is investigated as a solute-competitive mobile phase additive to intentionally block the hydrophobic cyclodextrin cavities on the stationary phase. By varying the concentration of ACA additive in the mobile phase, control over the retention and chiral recognition of the stationary phase is demonstrated.     

离子色谱-紫外检测法同时分析碘酸根、碘离子、溴酸根和溴离子

建立了同时分析碘酸根、碘离子、溴酸根和溴离子的离子色谱-紫外检测分析方法。用季铵型阴离子交换柱,以柠檬酸-乙腈为流动相,采用紫外检测器实现了4种离子的同时分离和检测。研究了检测波长和流动相种类、浓度、pH值等因素对4种离子分离和测定的影响,探讨了保留规律,优化了色谱分析条件。在检测波长为210 nm、流动相为1.0 mmol/L柠檬酸-乙腈（85：15,v/v;pH 5.0）、流速为0.9 mL/min、柱温为40 ℃条件下,4种离子完全分离,且系统峰不干扰测定。4种离子的检出限（S/N=3）为0.07~0.16 mg/L,连续5次进样测定的峰面积和保留时间的相对标准偏差均在1%以下。将此方法用于离子液体样品及地下水样品的分析,结果准确、可靠。     

Preparation and ion chromatographic properties of a new core-shell chromatographic support Al2O3/SiO2-10

A new stationary phase Al₂O₃/SiO₂-10 was prepared and characterized by XPS, XRD, SEM and surface analysis. The anion exchanger properties of this new stationary phase were investigated by the separation of inorganic anions in ion chromatography (IC). pH of the mobile phase, concentration and strength of the Lewis base of the elute, and the organic modifier of the mobile phase strongly affect the separation of inorganic anions, and anion exchange selectivities of the analyte on the new support are significantly different from quaternary ammonium styrene based anion exchangers. The result of separation of inorganic anions shows that the new stationary phase provides excellent column efficiency, well-defined chromatographic peaks and favorable retention times.     

Anion chromatography with a crown ether-based stationary phase and an organic modifier in the eluent

The unique ability of macrocyclic ligands, such as the crown ethers and cryptands, to selectively complex alkali metal cations can be used as the basis for chromatographic separations of anions. Specifically, macrocycles which are adsorbed onto a reversed-phase column, form positively charged anion-exchange sites when they combine with eluent cations. Previously we have demonstrated gradient anion separations based on changing the column capacity during the course of the separation by altering the eluent cation, temperature, or organic modifier content using cryptand-based columns. Herein we report that excellent separations can also be achieved using 18-crown-6 based columns. In this column, anion retention increases with increasing eluent strength and organic modifier content. This observation is in keeping with the relatively moderate affinity of crown ethers for alkali metals when compared to cryptands. The separation of anions achieved by optimizing mobile phase variables shows that isocratic separations of anions on the crown-based column are almost as good as separations achieved only under gradient conditions on cryptand-based columns. Cation gradients provide additional improvements on the separations using the crown-based column.     

Evaluation and application of liquid chromatographic columns coated with 'intelligent' ligands: (I) acylcarnitine column

Unique stationary phases of octadecylsilica (ODS) coated with acylcarnitines have been developed for liquid chromatographic columns. The ODS column coated with acylcarnitine was readily prepared by recycling the solution containing acylcarnitine through an ODS column in a closed loop. Acylcarnitine was adsorbed on the ODS surfaces by hydrophobic interaction between the acyl group of acylcarnitine and the octadecyl group of the ODS phases. The ODS column coated with stearoylcarnitine (CN-18 column) was the most stable among the four columns coated with acylcarnitines of various acyl chain lengths (decanoylcarnitine, lauroylcarnitine, myristoylcarnitine, and stearoylcarnitine) under the condition of delivery of the mobile phase, indicating that adsorption of acylcarnitine on the ODS surfaces depended on the length of acyl chains. The CN-18 column was usable for delivering the mobile phase contained less than 20% (v/v) acetonitrile, retaining almost the same separation efficiency as the intact ODS column. The retention behavior of ionic solutes on the CN-18 column could be explained by both ionic and electrostatic interactions between the solutes and the stationary phase. The CN-18 column enabled efficient separation of inorganic anions, nicotinic acids, amino acids, and nucleotides. The chiral ODS column coated with enantiomer of stearoylcarnitine, L-stearoylcarnitine (L-CN-18 column) could achieve direct enantiomeric separation of DL-tryptophan, alpha-methyl-DL-tryptophan and DL-3-indolelactic acid using 100% water as the mobile phase. The L-CN-18 column could also separate enantiomers of amino acids and alpha-hydroxycarboxylic acids by ligand-exchange chromatographic mode using a mobile phase containing copper(II) ion. The chiral recognition is discussed for enantiomeric separation on the L-CN-18 column.